Swine influenza is an acute respiratory infection of pigs caused by influenza A virus (IAV) of Orthomyxoviridae family. At present H1N1, H1N2 and H3N2 subtypes of IAV cause majority of infection in pigs. Owing to the presence of both avian (α2,3 Gal) and human (α2,6 Gal) IAV receptors, pigs can potentially act as mixing vessel for different IAV. Acute clinical signs in influenza infected pigs include high fever, anorexia, respiratory distress, nasal discharge and coughing. Influenza causes significant economic loss in the pig industry through morbidity, loss of body weight gain, increased time to market, susceptibility to secondary bacterial and viral infections like mycoplasma and porcine reproductive and respiratory syndrome (PRRS), medication and veterinary expenses. Some of the swine influenza virus (SwIV) can also be transmitted from pigs to humans creating public health risk. For example, the 2009 H1N1 swine influenza virus infected approximately 20% of the global population and caused around 200,000 deaths, in addition to approximately 500,000 deaths due to seasonal annual influenza infection.
Vaccination is one of the most effective means of controlling influenza. At present swine influenza vaccines are commercially available to use in pigs. Due to high mutation rates in circulating influenza viruses in animals the efficacy of commercial vaccines in the field is always poor. Commercial multivalent vaccines coadministered with an adjuvant intramuscularly as prime-boost strategy provide homologous, but weak heterologous protection. Intramuscular vaccination does not induce the required levels of local mucosal antibody and cellular immune responses; moreover, there are reports of inactivated vaccine associated enhanced respiratory disease. Thus, persistent economic burden of swine influenza in pig industry and its potential risk of zoonotic transmission to humans warrants the development of broadly cross-protective vaccine platforms.